Method of getter flashing



June 15, 1965 .1.B. Fl'rzPATRlcK Erl-Al.y g 3,189,397

METHOD 0F GETTER FLASHING Filed Feb. 28. 1961 United States Patent O3,189,397 METHOD OF GETTER FLASHWG John B. Fitzpatrick, Essex County,NJ., and William O. Zvonik, Flushing, FLY., assignors to RadioCorporation of America, a corporation of Delaware Filed Feb. 23, 1961,Ser. No. 92,245 2 Claims. (Cl. Sid-25) This invention relates toelectron tube mounts in which space allocations are relatively limited,and to a novel method of flashing a getter for increased yield of activegetter material.

One type of electron tube in which the invention iinds particularutility is generally known as a pencil tube. This tube comprises anelongated envelope including two metallic end portions. In one of themetallic end portions is housed a complement of cylindrical electrodesdisplosed concentric relation, and in the other end portion are locateda getter structure as well as getter and heater supports in the form oflead-in wires or conductors.

One of the problems involved in housing the supports for the heater andgetter structure, as well ash the getter structure itself, in theirassociated tube end portion, concerns the space available for thispurpose. Since the inner diameter of this portion is only aboutthree-sixteenths of an inch, suitable space allocation for the severalsupports and the getter structure, with assurance of freedom fromundesirable electrical shorts therebetween, presents a seriousdiliiculty. t

Another problem is related to the getter structure. Due to therelatively large amount of metal used in the construction of a penciltype tube, an appreciable amount of residual gas remain occluded in themetal after tube seal-off. The getter is relied on to take up such gasduring the life-time of the tube. Consequently a relatively large amountof active getter material is needed to produce a tube having a desiredlong service life. In some applications, Such as use in satellites, itis desirable that the tube have an operating life as long as twenty-flvethousand hours.

One known way of evolving a relatively large amount of gas absorbingmaterial from a getter ilash is by reliance on an exothermic reaction ofthe material of which the getter is composed. However, such exothermicreaction occurs only when the getter material is raised to a relativelyhigh temperature.

Heretofore, in tubes of the type discussed, it has not been feasible toheat a getter having the desired amount of` active getter material forthe long life indicated, to a required tlashing temperature, for severalreasons. The getter structure for a pencil tube must necessarily be of atype heated by electrical power fed to it directly by electricalconductors. This is a consequence of the metallic enclosure of theregion in which the getter is located, which makes it impossible to heatthe getter by induction from an exterior source. Sincethe regionreferred to is hermetically sealed from the ambient, it is necessary forthe electrical conductors to be hermetically sealed through the wall ofthe enclosure. The seal is effected through the insulating headeraforementioned.

The relatively small diameter of the insulated header requires the useof conductors of relatively small cross section. Such small crosssection of the conductors limits the amount of electrical power that canbe carried safely thereby preserving the seals through the header fromdamage. This limit in power carrying ability is below that required forashing a getter having the desired amount of active getter material forrelatively long tube life.

Accordingly it is an object of the invention to provide an improvedelectron tube.

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A further purpose is to provide an improved method of flashing a getter.

Briefly considered, a getter mount according to the in-` ventioncomprises lead-in conductors sealed through an insulating header andconnected to spaced portions of a` getter structure. The cross-sectionalarea of the getter structure is relatively large in order to contain asutiicient amount of active getter material for relatively long tubelife. The cross-sectional area of the conductors is relatively small toavoid the development of objectionable strains in the header, and toconserve space within the tube envelope. Thus, the relationship betweenthe cross-Sectional areas of the getter structure and the conductors isunfavorable to seal preservation during the passage through theconductors of electrical power suflicient to flash the getter.

According to one aspect of the invention a novel method of dashing thegetter is provided which renders the aforementioned relationship betweenthe cross-sectional areas of the conductors and getter structure,favorable with respect to seal preservation. This makes it feasible tohouse conveniently a relatively large getter structure within arelatively small space provided in the tube. An important contributionto this feasibility resides in the fact that the lead-in conductors donot require enlargement of their cross-sections, Consequently, theconductors do not impose an added accommodation burden on the relativeiysmall space aforementioned.

Briefly stated, the novel method. of the invention involves cooling thelead-in conductors and the header while the getter structure isenergized to flashing temperature, the cooling being continued for ashort time after v flashing to remove residual heat from the getterstructure.

One way, by way of example of the invention, in which the cooling may beaccomplished is by immersing the entire tube including the exteriorportions of its leadin conductors, in a relatively cool insulatingliquid such as deionized water, during the liashing operation.

The cooling step aforementioned prevents the lead-in conductors fromreaching a temperature at the seal regions high enough to harm theseals. In the absence of such cooling the relatively large amount ofpower conducted by the lead-ins to, and as required for flashing by, therelatively large getter structure, would raise the conductors to atemperature adverse to the seals.

Further objects and features of the invention will become apparent asthe present description continues.

Reference to the drawing for a more detailed considera tion of anexample embodying the invention, will reveal that:

FIG. l is a fragmentary elevational view, partly in section, of anelectron tube having a getter mount incorporating the invention;

FIG. 2 is a transverse sectional View taken along the line 2 2 of FIG.1;

FIG. 3 shows an enlarged cross-section of the getter, taken along theline 3--3 of FIG. l; and

FIG. 4 shows an elevation partlyl in section, of apparatus useful inpracticing the method aspect Iof the invention.

There are two known complementary techniques for removing gases from theenvelopes of electron tubes. One is by pumping the gases out through anexhaust tubulation communicating with the interior of the tube. Theother is by the action of a getter within the tube envelope, which,after sealing the exhaust tabulation, is heated to release a material,such as barium, for chemically combining with any gas remaining orevolved within the envelope.

To perform its function of reacting with gases within the tube envelope,it is necessary that the getter be heated mais? to a hashingtemperature, at which it releases its gas absorbing material. Where thegetter is disposed in an envelope having a glass portion surrounding thegetter, it is customary to raise the getter to its hashing temperatureby inducing radio frequency energy therein by a coil positionedexteriorly of the envelope. However, where the envelope portionsurrounding the getter is made of a metal that shields the getter fromexteriorly applied radio frequency energy, it is customary to connectspaced portions of the getter structure to electrical conductors thatare sealed through the tube envelope, and to subject the conductors to apotential difference. in this way, electrical current is fed through thegetter structure and as a consequence of the dissipation of electricalenergy therein, the getter structure is raised to the desired flashingtemperature.

The amount of getter material in the getter structure is a significantfactor in the life duration of an electron tube. If a relatively smallamount of getter material is provided, its full depletion will occurwithin a relatively short time, and the subsequently evolved gases willbe free to adversely affect tube operation.

One tube type that is particularly adapted for use in satellites byvirtue of its relatively rugged structure, is the so-called pencil tube.This type of tube, an example of which is shown in FIG. 4, includes ametal end portion or sleeve 12 housing the getter structure 14. Thegetter structure is supported on lead-in conductors 15, 18 passingthrough a disc shaped header 20 made of soft glass or ceramic (FIG. 1).For reasons of economy, most pencilV tube types employ headers of softglass, such as Corning Glass No. 0120. The lead-in conductors 16, 18

Vare of a type known as Dumet which comprises a structure including acore of an alloy of iron and nickel and a sheath Iof copper.

As a consequence of the metallicenclosure of the getter structure by thesleeve 12, which may be made of steel, it is necessary to heat thegetter 14 to flashing temperature by passing electrical currenttherethrough by means of the conductors 16, 18. Heretofore, the amountof current that could be passed through the conductors 16, 1% waslimited to a value sufficiently low to preserve from harm the sealsformed between the header 20 and the conductors 16, 18. This currentvalue was 4.2 amperes at 2 volts. This limitation restricted the getterto a cross-section of relatively small size, in order to produce therequired characteristic resistance of about 10 ohms per meter, requiredfor getter flashing. A tantalum ribbon having the aforementionedresistance and cut to the specific length required was capable ofcontaining only from 0.4 to 0.6 milligram of getter material such asbarium berylliate.

The foregoing limitation on the amount of getter material yield wasaccounted for in the case of tubes having headers of soft glass of thetype described, by the strainpoint temperature of such glass and itscoefficient of expansion. The strain-point temperature of the glassdescribed is about 395 C. At this temperature strains may be introducedinto the glass body of the header. Some of such strains may be harmfulto header stability. The coeicient ofV expansion of Corning Glass No.0120 is about S9 10-'l inches per inch per degree centigrade, while thelongitudinal coecient of expansion of the Dumet conductors is 65 l0*7inches per inch per degree centigrade. This difference in expansioncharacteristics between the header and conductors is harmful to theseals between the conductors and the header, when the conductors areheated to an appreciable temperature.

According to the invention there is provided a getter structure adaptedto yield 5 milligrams of free barium for a pencil type tube, and to usea power input of from 20 to watts, involving a current of 13 ampereswithout enlarging the cross-section of the conductors 16, 18. Thisrepresents an increase in getter material yield of about 2,500 percentabove that heretofore obtainable, and conl ributes to the attainment ofa tube life of the order of 25,000 hours.

The getter mount according to the invention includes a header 20, whichmay be made of Corning Glass No. 0120 for example, through which Dumetleads 16, 1S, 22 and Z4 are sealed (FIGS. 1 and 2). The Dumet leads areof a size heretofore used, Le., 20 mils in diameter. The header 20 has adiameter of about 0.2 inch and is about 0.08 inch thick. Lead-inconductor 16 serves exclusively as a conductor and support for thegetter structure 14. Lead-in 13 serves the dual function of conductorand support for the getter structure and as a conductor for the heater26. lead-in 22 is connected only to the heater 26. Lead-in 24 (FG. 2)serves the sole function of providing a symmetric array of lead-ins inthe header to balance any strains in the glass of the header produced bythe other lead-ins. lts inner end terminates ush with the upper surfaceof header 20 (FIG. 1). its outwardly extending portion 28 is cut offprior to the completion of the tube. Lead-in 24 serves to preserve apredetermined strain pattern in the header, thereby conditioning theheader to withstand without harm, mechanical and temperature shocks.

Lead-in 18 serves as the common conductor for the getter structure 14and header 26 in the interests of space economy within the sleeve 12.Such economy is mandatory in View of the relatively large size of thegetter structure 14. If the lead-in 24 were elongated to engage theupper end of the getter structure as viewed in FlG. 1, to provideindependent leads for the heater and getter, it would render the regionwithin the sleeve 12 so cramped that electrical shorts between theseveral conductors therein might occur.

The getter structure 14 (FIG. 3) includes a sheath 30, which may be madeof iron and within which is disposed a body 32 comprising a matrix ofnickel impregnated with a barium yielding material such as abarium-aluminum alloy, which contributes to an exotherrnic reaction, orthe material may be barium alone. Any other active source of barium maybe used.

The getter sheath 30 includes a thinned down portion 34 extendingbetween shoulders 36, 3S formed in the sheath. The thickness of thethinned down portion 34 is about 0.002 inch, while the thickness of theother portions of the sheath 30 is about from 0.010 to 0.015 inch.

The thinned down portion 341 of the getter sheath constitutes a zone ofweakness which ruptures during getter flashing. Such rupture occurspartly as a consequence of volatilization of the material of the thinneddown portion in response to heat generated therein by the flashingcurrent, and partly in response to pressures created by the getter body32 when heated by the sheath. The shoulders 36, 3S constitute effectivemeans for properly directing the flash of the appreciably increasedvolume of active getter material, to a region in which it is harmless totube operation. lt is preferred that the getter structure 14 be disposedsubstantially parallel to the axis of sleeve 12. In this way the gettermaterial expelled by the ash will impinge on the inner wall of thesleeve 12 and assure absence of getter material on the inner surface ofheader 20 and on the lower surface, as viewed in FIG. l, of a spacingdisc 40, made of mica for example, and Serving to space heater leads 18and 22 from each other. Such absence of getter material on the surfacesreferred to precludes current leakage thereacross between conductorshaving different potentials.

While the current carrying capacity of the getter conductors 16, 18 isadequate for a getter structure of relatively small size and containingfrom 0.4 to 0.6 milligram of getter material, it presents a seriousproblem in connection with a getter adapted to yield 5 milligrams ofgetter material, and requiring appreciably more electrical current forhashing.

This problem arises because as indicated before herein,

the conductors in each case are restricted to a diameter of mils. inorder to avoid an undesirable strain pattern in the header, and in theinterests of space economy within the sleeve 12. Prior getter structuresyielding relatively small amount of getter material referred to,comprised a tantalum ribbon or trough having a relatively smallcross-section characterized by a resistance of about 10 ohms per meterand were limited to a power input of from 2 to 10 watts. The getterstructure according to the invention, on the other hand, comprises asheath of material such as iron and having a relatively largecross-section involving a resistance of only 1.3 ohms per meter. Sincethe conductors for both getter structures are required to be of the samesize, as pointed out above, it is obvious that the dissipation ofelectrical energy must be greater for getter flashing, in the conductorsserving the larger getter than in those serving the smaller getter. Itwas found that the energy dissipated in the conductors associated withthe smaller getter were such as to heat the conductors to a temperaturebelow 395 C., the strain-point temperature of the glass header. However,the energy dissipated in the conductors serving the larger getterrequired a power input resulting in a temperature in the conductors ashigh as 800 C. Such high temperature was harmful to the seals betweenthe conductors and the header through which they pass and could not betolerated in the manufacture of electron tubes.

According to a method aspect of the invention, the foregoing difficultyis avoided. According to this method aspect, the tube 10 (FIG. 4) isevacuated to a desired degree by a suitable pumping system (not shown)and an exhaust tubulation 42, made of copper for example. After exhaust,the exhaust tubulation is sealed ohc by urging together opposite wallportions thereof with sucient force to produce a weld therebetweenwithout the deliberate application of heat. Thereafter the tube l0 issuspended in a beaker 44 made of glass for example, and containing acooling liquid 46. The suspension of the tube in the beaker is effectedby engagements between clamps 48, S0 and conductors 1S, 15 respectively.The clamps 48, 50 are xed to conducting rods S2, 54 respectively. Therods are adjustably mounted on an insulating support 56, and accordingto one example, are connected to a power supply (not shown) of 11amperes at 2 volts. A switch 58 is adapted to selectively connect anddisconnect the conducting rods 52, 54 from the power sourceaforementioned.

A getter dashing operation according to the invention is effected byclosing switch 58 for about six seconds, with the tube 10 suspended inthe cooling liquid as aforementioned. It is found that this interval oftime is long enough to tiash the getter, whether it be of the exothermictype or of the endothermic kind. lt is further found that during thisperiod, the leads 16, 18 do not heat up to a temperature adverse to theconductor seals.

Since the energization of the getter structure 14 (FIG. 1) to ashingtemperature involves heating the sheath 30 thereof (FIG. 3) to atemperature sufciently high to fuse the thinned down portion 34 thereofand vaporize the active getter material 32, it is found necessary toallow the tube 10 to remain in the cooling fluid 46 for about a minuteafter the switch 58 is opened, to allow residual heat in the sheath tobecome dissipated by conduction through the conductors 16, 18 to thecooling fluid. Without such dissipation of the residual heat in thesheath 30, there is danger that this residual heat might harm theconductor seals aforementioned.

The cooling liquid 46 should be non-electrolytic and possess goodthermal capacity. Deionized water is preferred. While methanol can beused, its use involves undesirable hazards. Oil can also be used, but itinvolves a re-cleaning problem.

The liquid 46 should be kept at a cool temperature. Room temperature hasbeen found to be adequate, but temperatures from appreciably below roomtemperature to as high as C. are tolerable. However, a temperature of 75C. is about the upper limit of the temperature range that can be usedfor good results.

The beaker 44, in one example had a capacity of 2 liters. This permitteduse of a sufficient quantity of cooling liquid for successively fiashinga relatively large number of electron tubes without raising the liquidto an intolerably high temperature. To keep the liquid cool it may bereplaced at intervals or the liquid may be circulated from a relativelylarge reservoir. Cooling means may also be used for cooling the liquid.If desired, a trough may be used instead of a beaker to permit thesimultaneous ilashing of a plurality of electron tubes.

What is claimed is:

1. Method of dashing a getter structure, wherein the getter structure isdisposed within an envelope having a glass portion and two lead-inconductors sealed through said glass portion in glass-to-metal seals areconnected to spaced portions of said getter structure and have legsextending exteriorly of said envelope, said method comprising suspendinga portion of said legs in a relatively 'i cool non-electrolytic liquidwhile engaging said two lead in conductors only, passing electricalpower through said conductors of a magnitude normally accompanied byheat harmful to said glass-to-metal seals of said conductors throughsaid envelope in the absence of cooling by said liquid, said liquidserving to cool said conductors at the regions of said seals to atemperature harmless to said seals, stopping the passage of electricpower through said conductors after said getter has dashed, continuingthe immersion in said liquid of said leg portions after said stoppage ofsaid electrical power through said conductors, for dissipating residualheat in said getter structure, and removing said legs from said liquidafter said residual heat has been dissipated.

2. Method of ilashing within a metal envelope of an electron tube, agetter having two getter leads connected thereto and whose flashingtemperature is as high as the temperature which can be achieved only byelectric current of a value sufficiently high to heat a portion of saidgetter leads adjacent to said envelope to a temperature adverselyatfecting the subsequent operation of said tube, said method comprisingsuspending said electron tube by said two getter leads only, in adielectric liquid at substantially room temperature, at a depth todispose a portion of said leads adjacent to said envelope in saidliquid, applying electric current to said getter leads of a value togenerate suilicient heat to raise the temperature of said getter to saidflashing temperature while said portion of said leads is immersed insaid liquid, stopping the application of electric current to said leads,and then removing said tube from said liquid prior to said subsequentoperation of the tube and after residual heat in said getter has beendissipated by conduction through said leads to said liquid.

References Cited by the Exaer RALPH NEILSON, Examiner.

1. METHOD OF FLASHING A GETTER STRUCTURE, WHEREIN THE GETTER STRUCTUREIS DISPOSED WITHIN AN ENVELOPE HAVING A GLASS PORTION AND TWO LEAD-INCONDUCTORS SEALED THROUGH SAID GLASS PORTION IN GLASS-TO-METAL SEALS ARECONNECTED TO SPACED PORTIONS OF SAID GETTER STRUCTURE AND HAVE LEGSEXTENDING EXTERIORLY OF SAID ENVELOPE, SAID METHOD COMPRISING SUSPENDINGA PORTION OF SAID LEGS IN A RELATIVELY COOL NON-ELECTROLYTIC LIQUIDWHILE ENGAGING SAID TWO LEAD IN CONDUCTORS ONLY, PASSING ELECTRICALPOWER THROUGH SAID CONDUCTORS OF A MAGNITUDE NORMALLY ACCOMPANIED BYHEAT HARMFUL TO SAID GLASS-TO-METAL SEALS OF SAID CONDUCTORS THROUGHSAID ENVELOPE IN THE ABSENCE OF COOLING BY SAID LIQUID, SAID LIQUIDSERVING TO COOL SAID CONDUCTORS AT THE REGIONS OF SAID SEALS TO ATEMPERATURE HARMLESS TO SAID SEALS, STOPPING THE PASSAGE OF ELECTRICPOWER THROUGH SAID CONDUCTORS AFTER SAID GETTER HAS FLASHED, CONTINUINGTHE IMMERSION IN SAID LIQUID OF SAID LEG PORTIONS AFTER SAID STOPPAGE OFSAID ELECTRICAL POWER THROUGH SAID CONDUCTORS, FOR DISSIPATING RESIDUALHEAT IN SAID GETTER STRUCTURE, AND REMOVING SAID LEGS FROM SAID LIQUIDAFTER SAID RESIDUAL HEAT HAS BEEN DISSIPATED.